In message <[email protected]>, dated Tue, 15 Jan 2008, "Tarver, Peter" <[email protected]> writes:
>My lack of conviction is based on the numbers in Annex J not matching >*any* of the electrochemical tables I've reviewed (not thousands, but >many tens, perhaps a couple hundred). I'm unconvinced that the table >is based on any valid scientific studies. Further down, you said that the tables you reviewed relate to brackish or sea water. I entirely agree that the Annex J table doesn't apply under those conditions. As I indicated, it applies only under strict laboratory conditions, in the absence of all anions, such as chloride and sulfate. The concentration of any soluble or gaseous participant in the electro-chemistry matters as well. I have some data from 'Kaye and Laby' 14th edition (old), which is indicative. The standard electrode potential (SEP) of silver versus hydrogen (taken as the 0 V reference) is 0.8 V, but if chloride ions are present, the value drops to 0.22 V, indicating an increased tendency to corrode. Several of the data points in Annex J (of IEC/EN 60950-1:2001, which does not have the typos corrected [1]) relate to alloys, and reliable SEP values of these are notoriously difficult to ascertain. When I wrote 'true', I meant that the numbers are internally consistent (except for the typos), which you can check by considering a triangle of 3 different materials - the net voltage round the triangle (carefully taking polarity into account) must be zero. What we don't know is what concentrations were assumed. I've also just discovered that the typos have been 'dis-corrected' in the latest draft of IEC 62368! -- OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk For very important information, please turn over. John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
